THE DIGESTION OF THE FOODSTUFFS 129 



gastric juice, while the function of the pepsin is to render the 

 proteid capable of being split up and it therefore only aids the 

 action of the acid. 



The action of the hydrochloric acid is, however, not a fermenta- 

 tive action, as is the case in the formation of sugar from starch 

 where a small quantity of acid can split an unlimited amount of 

 starch. In the proteid digestion, the acid is used up, for it forms 

 with the digestion products the acid proteoses-chlor-hydrates and 

 thus becomes inactive. Pepsin, as ferment, is unlimited in its 

 action. 



Pepsin, a ferment of proteid-like composition, is destroyed 

 by heating, by strong alcohol, and by small quantities of 

 free alkali. The last, however, does not act thus in the 

 presence of undigested proteid, perhaps because the pepsin 

 unites with the proteid. 



To obtain pepsin, extract the mucous membrane of the stomach, 

 especially that of the antrum, with glycerin or with a 0.2$ to 0.4^ 

 hydrochloric acid solution. 



The intermediate products thereby formed successively by 

 peptic digestion of proteids are: 



1. A precipitate formed by neutralizing the solution. 

 Among the first products of peptic digestion, especially in 

 that of coagulated proteids, there is present a proteid coagu- 

 lated by heat, which, however, soon undergoes a still further 

 change. 



2. Primary albumoses, protalbumose and heteroalbu- 

 mose, precipitated from neutral solutions by saturation with 

 NaCl. 



3. A deuteroalbumose, which is precipitated from acid 

 solutions by saturation with NaCl. 



4. A deuteroalbumose, precipitated by saturation with 

 ammonium sulphate. 



5. Peptones, not precipitated by ammonium sulphate (see 

 page 37). 



During peptic digestion, not all the proteid is completely 

 changed to peptone ; the amount of the resulting peptone is, 

 e.g. in case of the crystallized serum albumin of horse blood, 

 only about one-half that of the original proteids ; the residue 

 remains in the form of deuteroalbumose. 



